What exactly does next choice do?

Ok, so I've taken next choice twice and plan-b once because of my psychopath-ness lol :) and the first time I took it, I got my period at the right time (I dont remember when I took it but I got it on the 18th of Feb and it lasted 3 days like my periods always do) March I got my period the 22nd and it lasted to the 25th. When I took Plan-b I got my period 3 days late and I took it around when I was supose to be ovulating and got it June 4th and ended the 8th. I took Next choice at 12pm today and I'm going to take the next one in a little but am I around the time I should be ovulating? Im not really sure now that I was late. I had sex the other night but he never came in me. And I know there's studies that show when you take the pill before ovulating/during/after, it would come on time/early/late. So if ya'll could just give me your opinion that'd be great :) and what does the pill exactly do? I know it does like 3 things but I lost the box and I couldn't find it online. kthx<3